.TH std::ranges::iter_swap 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::iter_swap \- std::ranges::iter_swap

.SH Synopsis
   Defined in header <iterator>
   namespace ranges {

       inline namespace /* unspecified */ {                              \fI(since C++20)\fP
           inline constexpr /* unspecified */                            (customization
               iter_swap = /* unspecified */;                            point object)
       }

   }
   Call signature
   template< class I1, class I2 >
   constexpr void iter_swap( I1&& i1, I2&& i2 ) noexcept(/* see below    \fI(since C++20)\fP
   */);
   Helper function
   template< class X, class Y >

   constexpr std::iter_value_t<X>
       iter-exchange-move( X&& x, Y&& y )                                (exposition
                                                                         only*)
   noexcept(noexcept(std::iter_value_t<X>(std::ranges::iter_move(x)))
   &&

                noexcept(*x = std::ranges::iter_move(y)));

   Swaps values denoted by two iterators.

   The effect of the exposition-only helper function iter-exchange-move is equivalent
   to

 std::iter_value_t<X> old(std::ranges::iter_move(x));
 *x = std::ranges::iter_move(y);
 return old;

   ranges::iter_swap(i1, i2) is expression-equivalent to:

    1. (void)iter_swap(i1, i2), if i1 or i2 has a class or enumeration type and the
       expression is well-formed, where the overload resolution of iter_swap is
       performed with the additional candidate void iter_swap(auto, auto) =
       delete;^[1], excluding std::ranges::iter_swap itself.
          * If the selected overload does not exchange the value denoted by i1 and i2,
            the program is ill-formed, no diagnostic required.
    2. Otherwise, ranges::swap(*i1, *i2) if both I1 and I2 model indirectly_readable
       and if std::iter_reference_t<I1> and std::iter_reference_t<I2> model
       swappable_with.
    3. Otherwise, (void)(*i1 = iter-exchange-move(i2, i1)), if
       std::indirectly_movable_storable<I1, I2> and
       std::indirectly_movable_storable<I2, I1> are both modeled, except that i1 is
       only evaluated once.
    4. Otherwise, ranges::iter_swap(i1, i2) is ill-formed, which can result in
       substitution failure when ranges::iter_swap(i1, i2) appears in the immediate
       context of a template instantiation.
    1. ↑ This precludes calling unconstrained std::iter_swap.

  Customization point objects

   The name ranges::iter_swap denotes a customization point object, which is a const
   function object of a literal semiregular class type. For exposition purposes, the
   cv-unqualified version of its type is denoted as __iter_swap_fn.

   All instances of __iter_swap_fn are equal. The effects of invoking different
   instances of type __iter_swap_fn on the same arguments are equivalent, regardless of
   whether the expression denoting the instance is an lvalue or rvalue, and is
   const-qualified or not (however, a volatile-qualified instance is not required to be
   invocable). Thus, ranges::iter_swap can be copied freely and its copies can be used
   interchangeably.

   Given a set of types Args..., if std::declval<Args>()... meet the requirements for
   arguments to ranges::iter_swap above, __iter_swap_fn models

     * std::invocable<__iter_swap_fn, Args...>,
     * std::invocable<const __iter_swap_fn, Args...>,
     * std::invocable<__iter_swap_fn&, Args...>, and
     * std::invocable<const __iter_swap_fn&, Args...>.

   Otherwise, no function call operator of __iter_swap_fn participates in overload
   resolution.

.SH Example

    This section is incomplete
    Reason: no example

.SH See also

   iter_swap swaps the objects pointed to by two adjusted underlying iterators
   (C++20)   \fI(function template)\fP
   iter_swap swaps the objects pointed to by two underlying iterators
   (C++20)   \fI(function template)\fP
   iter_swap swaps the elements pointed to by two iterators
             \fI(function template)\fP

.SH Category:
     * Todo no example
